Agilent Unveils Optical Switching Breakthrough
BALTIMORE, MD--What could turn out to be a significant breakthrough in optical switching technology was unveiled here at the Optical Fiber Communications (OFC) exhibition yesterday (March 7).
Agilent Technologies Inc. http://www.agilent.com showed a 32 x 32 and a 32 x 16 port switch that uses tiny bubbles to deflect light from one path to another at speeds of under 10 milliseconds. The technology competes with micro-electro-mechanical systems (MEMS) – arrays of microscopic mirrors – and has the advantage of having no moving parts to seize up or wear out. It also contains the light within the device, unlike some MEMS equipment, making it less prone to problems.
Agilent is packaging its so-called Photonic Switching Platform devices so they can be used by vendors to build switches. Large numbers of them can be connected together to offer carriers a step-by-step approach to expanding the capacity of optical cross connects, according to John J. O’Rourke, general manager of Agilent’s optical networking division.
News of Agilent’s announcement leaked out on Monday, resulting in a whopping 40 point increase in the company’s share price -- equivalent to a $20 billion increase in its market cap. “I’m astounded,” Don W. Smith, vice president and general manager of optical developments at Nortel Networks http://www.nortelnetworks.com told Light Reading afterwards.
Potential customers like what they’ve seen. “I think it’s great,” says Nicholas De Vito, vice president of product management and business development at Tellium Inc. http://www.tellium..com, a startup with a cross-connect that’s been designed to enable its switching fabric to be upgraded as new technologies evolve. “It’s got low losses, and they’ve got a really good story on reliability and scalability,” says De Vito. However, he reckons that it’ll take another six to nine months for Agilent’s technology to get to the point where vendors can start using it in their developments. And he believes it’ll take another six to nine months for commercial products to appear. The same goes for other optical switching technologies.
Right now, it’s unclear whether Agilent’s gear will scale to the 1000-plus port optical cross connects required by carriers. The number of devices needed to build a non-blocking cross-connect increases quickly as the port count goes up. A 512 x 512 port assembly would need 64 devices, according to David B. Andersen, R&D manager of Agilent’s optical networking division. The number of devices in larger assemblies could be reduced by making equipment that was only partially non-blocking, he adds.
Even so, light would have to pass through several devices, and each device would take its toll in reducing the strength of the signal by about 4.5 decibels. Andersen says this isn’t a problem; light signals are likely to be regenerated electrically when they come out of the cross-connect, for a variety of reasons.
Blowing bubbles The idea of using bubbles to switch light came to Julie Fouquet, an Agilent project manager, in an “a-ha!” moment in 1995, according to O’Rourke . She realized that the ink-pen technology already used by HP in its bubble jet printers could be re-used to solve many of the intrinsic problems of using mechanical devices to switch light.
How’s that? Agilent’s Photonic Switching Platform comprises two layers – a bottom layer of silica (glass) through which multiple streams of light signals travel and a top layer of silicon containing the ink-pen technology.
In the bottom layer, 32 parallel wave guides – microscopic trenches - are carved into the silica and intersect each other at an angle of around 120 degrees. The trenches are filled with a liquid with the same refractive index as the silica. Light passes straight through each of these trenches unless its interrupted by a bubble at one of the intersections, in which case it glances off into the trench crossing its path.
The bubble is created by tiny electrodes in the upper silicon layer of the device, The electrodes heat up the liquid to form a gas, in exactly the same way as in bubble jet printer technology. “It does it in microseconds and we only need to do it milliseconds,” notes O’Rourke.
The wave guides traverse the whole device, which means that unlike other optical switching devices it has ports on four sides. This has two big advantages, according to Andersen. First, it makes it easy to link together devices to create higher capacity switches. Second, it makes it easy to create add-drop muxes – equipment that peels off some wavelengths for local use while allowing other wavelengths to pass straight through.
Re-using bubble jet technology also promises big benefits. The same production process can be used, which will cut cost and reduce development time. Reliability also promises to be good, because million of ink pens have been manufactured and because ink pens are used much more intensively in printing than they will be when they’re used for switching.
On the other hand, ink pens are used in printing for making temporary bubbles, not bubbles that might have to be maintained in place almost permanently – as is the case with cross-connects. Having to do this will absorb quite a lot of electrical current and could lead to heat spreading across the device and interfering with other waveguides, according to one MEMS vendor, Chronos Integrated Microsystems, Inc. http://www.memsrus.com. Another MEMS vendor, Xros Inc. http://www.xros.com, denies Agilent’s claim that bubble jet-based switches will last longer because they have no moving parts. “We haven’t seen [the mirrors] wear out and we’ve conducted long-term tests,” says Tim Slater, principal scientist at Xros (see Xros Launches First 1000-Port All Optical Cross Connect).
-- by Peter Heywood, international editor, and Stephen Saunders, US editor, Light Reading http://www.lightreading.com